metamorphism and metamorphic rocks
DESCRIPTION
METAMORPHISM AND METAMORPHIC ROCKS. FACTORS INFLUENCING METAMORPHISM. PRESSURE. More pressure is exerted on rocks at depth than at Earth’s surface. LITHOSTATIC or CONFINING PRESSURE pushes on rocks in all directions. Grains become smaller and denser at depth. - PowerPoint PPT PresentationTRANSCRIPT
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
PRESSURE
More pressure is exerted on rocks at depth than at Earth’s surface.
LITHOSTATIC or CONFINING PRESSURE
pushes on rocks in all directions.
Grains become smaller anddenser at depth.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
PRESSURE
Pressure is greatest at thecontact point betweengrains.
Bonds can break.Ions migrate and re-bond.Rock becomes
compressed.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
PRESSURE
Pressure may be greater insome directions.
DIRECTED PRESSUREFlattens rock in the
direction at which thegreatest pressure isapplied.
Lengthens rock in the direction to the greatest pressure.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
PRESSURECauses existing minerals and
features to deform.Doesn’t affect minerals in
the rocks.
Induces FOLIATION, in which the tabular minerals are aligned to the direction ofgreatest directed pressure.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
FOLIATION
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
PRESSURE
For metamorphism to occur, 1 kilobar of pressure isrequired.1 Bar = pressure applied to the Earth’s surface
by the atmosphere.1 Bar = 1.02 kg/cm2
1 kilobar = 1000 Bar (or 1020 kg/ cm2)
These pressures occur at ~ 3 km depth.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
CIRCULATING FLUIDS
Water greatly influences metamorphism.Aids in migration of unbonded atoms and ions.Allows for exchange of ions between adjacent grains.
Water comes from a variety of sourcesGround waterSubducted oceanic crustCrystallization of magmaDecomposition of water-rich minerals like
amphiboles and clays
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
CIRCULATING FLUIDS
Influence production of new minerals by ionic exchange.
Speed up reactions and change overall composition of the rock.
METAMORPHISM AND METAMORPHIC ROCKS
FACTORS INFLUENCING METAMORPHISM
PARENT ROCK
Composition of parent rock influences the type of metamorphic rock produced.
METAMORPHISM AND METAMORPHIC ROCKS
TYPES OF METAMORPHISMCONTACT METAMORPHISM
Solid rocks in close proximity to magma will changein response to heating and circulation of hotfluids, i.e., INTRUSIONS.
Produces a “baked zone” in the adjacent country rock.Pressure is not significant in reaction.Impact of the intrusion is local.Only rocks in immediate contact with the intrusion
will be highly metamorphosed.
METAMORPHISM AND METAMORPHIC ROCKS
CONTACT METAMORPHISM
Minerals stable at high temperatures will be formed closest to the intrusion.
Coarser grained metamorphic minerals will also beformed closest to the intrusion.
Size of the intrusion also influences the amount ofmetamorphism.
Differences in temperature is also significant.
METAMORPHISM AND METAMORPHIC ROCKS
CONTACT METAMORPHISM
METAMORPHISM AND METAMORPHIC ROCKS
REGIONAL METAMORPHISMAlters rocks over a large geographic region.
Appalachians of New EnglandNorth Cascades of Washington-British Columbia
METAMORPHISM AND METAMORPHIC ROCKS
REGIONAL METAMORPHISM
BURIAL METAMORPHISM
Occurs deep in sedimentary basins.Requires depths > 10 km
At these depths and greater, lithostatic pressure andgeothermal heat drive metamorphic reactions andrecrystallization.
Does not require a tectonic process.Does not create mountain belts.Generally no foliation because no directed pressure.
METAMORPHISM AND METAMORPHIC ROCKS
REGIONAL METAMORPHISM
BURIAL METAMORPHISM
METAMORPHISM AND METAMORPHIC ROCKS
REGIONAL METAMORPHISM
DYNAMOTHERMAL METAMORPHISM
Affected by pressure (squeezing) and heat (magma).Occurs when converging plates squeeze rock caught
between the plates.Crust generally thickens.Surface rocks get taken deep into the Earth.Rocks are subjected to high temperatures, lithostatic
pressure and directed pressure.Rocks become foliated.
METAMORPHISM AND METAMORPHIC ROCKS
REGIONAL METAMORPHISM
DYNAMOTHERMAL METAMORPHISM
Produced metamorphic rocks found in the Alps,Himalaya, and Appalachian Mountains.
Also produced the greatly eroded metamorphic rocksin the Great Lakes region.
These rocks are exposed by uplift (faulting) and rapiderosion.
The process doesn’t reverse itself.
METAMORPHISM AND METAMORPHIC ROCKS
OTHER TYPES OF METAMORPHISM
HYDROTHERMAL METAMORPISM
Chemical alteration of pre-existing rocks by hot water.Occurs primarily beneath ocean floor near divergent
plate boundaries.Creates water-rich minerals.
Includes serpentine, talc, and chloriteIn addition, when steam hits ocean water and cools
rapidly, valuable metals such as Cu, Ni, Fe and Pb are precipitated.
METAMORPHISM AND METAMORPHIC ROCKS
OTHER TYPES OF METAMORPHISM
FAULT ZONE METAMORPISM
Produced by rocks grinding past each other at a fault.
Produced by directed pressure and frictional heat.
METAMORPHISM AND METAMORPHIC ROCKS
OTHER TYPES OF METAMORPHISM
SHOCK METAMORPISM
Produced by meteorite impact.Forms shock varieties of quartz.
StishoviteCoesite
METAMORPHISM AND METAMORPHIC ROCKS
OTHER TYPES OF METAMORPHISM
PRYOMETAMORPHISM
Results from ultra-high temperatures that occur in lowpressure environments.
Usually produced by lightning hitting surface rocks orsediments.
Fulgurite
METAMORPHISM AND METAMORPHIC ROCKS
OTHER TYPES OF METAMORPHISM
PRYOMETAMORPHISMFulgurite